The gloating Norwegian slayer flashed a right-wing salute in court as he was handed a 21-year sentence.

But the minimum he must serve is just 10 years.

And after educting the 445 days he has already spent behind bars, that equates to less than six weeks in jail for each of the 77 people he killed.

The judge’s “sane” ruling means he will be sent to prison rather than caged for life in a mental hospital. Breivik admitted blowing up the Oslo government HQ with a car bomb in July last year, killing eight people, before dressing as a policeman to slaughter 69 at a summer youth camp on Utoya island.

He also injured 242 others during his bomb and shooting spree.

Breivik, 33, smirked as he appeared in Oslo District Court yesterday.

Judge Wenche Elizabeth Arntzen said: “In a unanimous decision, the court sentences the defendant to 21 years of preventive detention.”

It is the maximum term that can be imposed in Norway although officials can keep him in jail indefinitely if he still poses a threat to the public.